The hindered amines have long been recognized as light and/or as thermal stabilizers for a host of organic materials subject to degradation induced by oxygen, heat or actinic light. The patent and academic publication literature is replete with references to these hindered amine compounds and their valuable stabilizing efficacies. There is no mention or suggestion in any of such references that the hindered amines themselves are also flame retardants per se.
Particularly relevant are U.S. Pat. Nos. 5,004,770; 5,096,950; 5,204,473; 5,300,544 and 5,844,026 as well as copending applications Ser. Nos. 09/257,711 and 09/253,161. These references pertain to various N-hydrocarbyloxy substituted hindered amines (so called NOR and NOROL hindered amines) and to various compositions stabilized therewith. As mentioned above, none of these reference disclose or even hint that the compositions stabilized with the NOR or NOROL hindered amines alone are flame retardant. This inherent property was never discovered, not even serendipitously, until the present invention was made. That this is so, is in itself evidence that even those of considerable skill in the hindered amine stabilizer art were quite surprised by this unexpected discovery. The fact that a large amount of an inorganic or organic classical bromine and/or phosphorus containing flame retardant could be substituted by a small amount of a NOR or NOROL hindered amine and still achieve very acceptable flame retardancy was also quite unexpected. This is highly beneficial for the environment and for safety reasons. Accordingly, polymeric substrate compositions made flame retardant by incorporating therein a synergistic mixture of a NOR or NOROL hindered amine plus a classic inorganic or organic bromine and/or phosphorus containing flame retardant is also quite surprising, unexpected and clearly not obvious to those of skill in this stabilizer art. This invention affords the public a valuable method for flame retarding polymers which cannot be gleaned from any of the prior art references.
U.S. Pat. No. 5,393,812 does describe polyolefin compositions which are made flame retardant by a combination of a halogenated hydrocarbyl phosphate or phosphonate ester flame retardant in combination with a alkoxyamine functional hindered amine, but there is no suggestion that the hindered amine itself is responsible for the flame retardancy, but rather that the hindered amine is preventing delustering and other undesirable effects from occurring in these polyolefin compositions.
European Application No. 0 792 911 A2, published after the filing date of the parent provisional application Serial No. 60/051,331, discloses that alkoxyamine functional hindered amines may have some flame retarding properties, but are quite effective when used to enhance the flame retarding efficacy of tris(trihalogenopentyl) phosphate flame retardants. This publication is somewhat ambivalent as to whether the alkoxyamine functional hindered amine are really themselves flame retardants in the absence of the recognized phosphate flame retardant.
The flame retardant (FR) market today is comprised of products which function to interfere with the combustion process by chemical and/or physical means. Mechanistically these FRs have been proposed to function during combustion of an article in either the gas phase, the condensed phase or both. The organohalogens are proposed to generate halogen species (e.g. HX) which interferes in the gas phase with free radical organic xe2x80x9cfuelxe2x80x9d from the polymer substrate. Synergists are proposed to react with HX to form additional chemical species with interfere with combustion in the gas phase, such as reaction of antimony oxide with HX to form antimony halide and water vapor. Still other flame retardant classes are proposed to impart efficacy in the xe2x80x9ccondensedxe2x80x9d phase such as forming a protective char layer on the polyester, or forming an intumescent or foaming on the polymer surface. The char or intumescent layer is thought either to prevent organic fuel from migrating from the polymer into the vapor phase where it can fuel combustion, or the char can act as a thermal shield to protect the underlying polymer article from thermally induced decomposition and generation of fuel. Phosphorus compound of various classes (e.g. halo- or non-halogenated) are an example. Further still, other classes of compounds are proposed to function in the condensed and/or vapor phase. Metal hydrates or metal oxides are proposed to generate water vapor under thermal conditions, the water acting to dilute the fuel mix in the combustion zone and to remove heat from the flame zone via conversion of water to vapor. Alumina trihydrate, magnesium hydroxide or oxide, and other compounds are reported to function in this way.
These state of the art chemistries described above have various detrimental aspects in addition to the effective flame retarding attributes mentioned. Certain organobrominated compounds are under governmental scrutiny for the generation of toxic by-products during the production or combustion such as dioxanes from polybrominated diphenyl oxides. Certain metal-containing flame retardants, notably antimony oxides, are under scrutiny for worker exposure and toxicity reasons. Antimony oxides often contain trace amounts of arsenic compounds which are suspected cancinogens. Overall, a growing concern has arisen regarding the generation of smoke and toxic gases which are evolved from these flame retardants during a fire. While the classic FRs may be effective combustion suppressants, the toxic gases they form pose a threat to human exposure.
The instant invention alleviates some of the detrimental aspects of the current state of the art which the use of large amounts of commercial flame retardants pose. The instant NOR or NOROL hindered amines are non-halogenated and free of heavy metals, thus avoiding generation of corrosive HX gases and avoiding exposure to toxic metals. In some applications, the instant invention provides a direct replacement for current FR systems where the instant NOR or NOROL hindered amine compounds provide a complimentary enhancment or synergistic system for heavy metals (e.g. antimony oxide replacement in ABS) where good flame retardancy can be achieved by using less classic FR agent in the presence of the instant NOR or NOROL hindered amine compound.